What causes porous eggs?

[laseterlass]

I have had 4 batches of eggs shipped to me this Spring. All of them have been porous and so far fertility has been very poor. I had 80% success with shipped eggs last year and I have 100% hatch of my own eggs that I incubate with shipped eggs. I have blood rings in most of the eggs a few days into incubation and read this occurs with porous shells.

 

[subhanalah]

In my experience (which isn't much) blood rings have been with eggs that had a ruptured yolk. Perhaps packing/handling of the eggs is at fault?

Not sure about the porous eggs, I got some too, I'll try to let you know how it goes, if I remember...it's still 20 days away!